This invention relates generally to an internal combustion engine and specifically to an exhaust gas recirculation cooling system.
Most internal combustion engines are met with the challenge of increasing power, increasing efficiency, and reducing emissions. Pressure charging an internal combustion engine both increases power and increases efficiency. Pressure charging is a process in which ambient air is compressed to allow more air to fill an engine cylinder. Numerous methods of pressure charging have been used including driving a compressor off an engine shaft.
Turbochargers are a pressure charging device that further improves efficiency by using energy in an exhaust gas to provide pressure charging. High pressure, high temperature exhaust gas enter a turbine connected to a compressor. As the high pressure, high temperature exhaust gas expands through the turbine, the turbine operates the compressor. As shown in U.S. Pat. No. 3,250,068 issued to Vulliamy on May 10, 1966 shows using turbochargers arranged in a serial fashion. This arrangement allows the turbochargers to be more responsive over a larger operating range. Further, arranging turbochargers in serial fashion provides opportunities for unique controls.
To reduce emissions, an exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles. EGR systems primarily recirculate exhaust gas from combustion into the intake air supply of the internal combustion engine. Exhaust gas introduced to the engine cylinder displaces a volume available for oxygen. Reduced oxygen concentrations lower maximum combustion temperatures within the cylinder and slow chemical reactions of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder. Burning the unburned hydrocarbons further reduces the emission of undesirable pollutants from the internal combustion engine.
In U.S. Pat. No. 5,142,866 issued to Yanagihara et al on Sep. 1, 1992, an exhaust gas recirculation system connects downstream from a first compressor in a first turbocharger. The first turbocharger connects serially with a second turbocharger. Serial turbocharging allows for more efficient compression of the intake air supply. The first turbocharger compresses a large volume of the intake air supply into a second volume. The second turbocharger is designed to compress the smaller second volume. Also, the second turbocharger is designed to respond quickly to changes in engine load.
Cooling recirculated exhaust gas further enhances emissions reductions available through recirculating exhaust gas. Cooling the exhaust gas prior to introduction into the engine cylinder further reduces the combustion temperatures in the engine cylinder. As with lower oxygen concentrations, the reduced temperature of recirculated exhaust gas ultimately lowers production of NOx in the engine cylinder.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention an internal combustion engine has an engine block connected with a cylinder head. An exhaust manifold and intake manifold fluidly connected with the cylinder head. A first turbocharger and second turbocharger fluidly connect with the exhaust manifold. An exhaust gas recirculation conduit fluidly connects the exhaust manifold with the intake manifold. A bypass conduit fluidly connects a compressed gas conduit feeding the intake manifold with at least one turbine of the turbochargers. An exhaust gas recirculation heat exchanger thermally connects the exhaust gas recirculation conduit with said bypass conduit.
In another aspect of the present invention, a method for controlling an exhaust gas recirculation system for an internal combustion engine senses an engine operating parameter. Where the engine operating condition indicates production or likely production of NOx, flow of exhaust gas is restricted through an EGR conduit. Further, flow of combustion air through a bypass conduit is also reduced. The flow of combustion air and the flow of exhaust gas exchange heat.